That's odd. Can you let us know what device/operating system and Spotify version you're currently using? On the other hand, give it a try reinstalling the app and see if you're still experiencing the same issue. Here's how.
I too have this same problem, and it drives me absolutely nuts nuts!! The repeat toggle turns itself on constantly, no matter how many times I turn it off. Over and over and over again. I havent been able to see it happen in the act, but rather I suddenly notice it has been turned once again, once I open the app again from the backgroud. Except mine toggles to ALBUM repeat, not song. I dont want the album to repeat when its done. Period.
Im using an iPhone 6SE, all apps on IOS up to date as of June 1 2017.
The same problem accurs on the OSX desktop app (running Sierra 10.12.5)
I'm having this same problem and it's very annoying. I listen to soft music or rain sounds when falling asleep, with just a few tracks in a playlist. Now that the repeat turns itself on, I wake up at 3 am, and it's still playing the same track. It's driving me crazy!!
I had the same problem with album repeat. I really like when I listen to an album and then the album radio comes on after. But no, it's always repeating the album. Today I had to toggle it off a couple times within minutes! I'm sick of it.